Thin-film transistors (TFT) are widely used, e.g., as switching elements in display devices. Thin-film transistors may thus control a gray level in display technology and may drive a variety of display devices. In a conventional display device, a semiconductor element for driving each pixel is formed of a thin-film transistor having at least one active layer. Thin-film stacks for use in TFTs may include transparent conductive oxide (TCO) films that are deposited onto substrates. TCO films have wide applications, as these TCO films may be used for electronic devices such as liquid crystal displays, touch panel devices, photovoltaic cells, and transparent thin-film transistors. As thin-film transistors are of increasing importance in many electronic devices, it is an issue to improve their electric properties and device performances.